Equal segregation of chromosomes to opposite poles during mitosis is essential for cell viability. To accomplish this chromosomes are condensed and attached to spindle microtubules at the centromere which coordinates the separation of sister chromatids at anaphase. Missegregation of chromosomes has been associated with many human diseases including several congenital disorders and nearly all forms of cancer. To better understand how chromosome segregation occurs we have begun to study the centromere in the freeliving soil nematode C. elegans. The centromere in C. elegans is approximately 10 times larger than it is in human cells making this system more amenable to cell biological studies. In addition functional studies can be carried out rapidly because it has recently become possible to eliminate gene functions using RNA mediated interference. My goal is to identify the proteins and DNA sequences involved in the assembly of the centromere and to identify the mechanisms involved in forming new centromeres. The approaches I will use are a combination of biochemical and cytological studies using RNAi and temperature sensitive mutants affected in these processes.